Field of the Invention
The invention relates to a signal processing apparatus, and more particularly, to a voice signal processing apparatus and a voice signal processing method.
Description of Related Art
In general, hearing-impaired people can clearly hear low frequency signals but have trouble receiving high frequency voice signals (e.g., a consonant signal). In the conventional technology, such issue is generally solved by lowering a frequency of the high frequency signal and overlapping signal frames. Since a time length is extended after lowering the frequency of the signal, it is required to use an interpolation method for calculating signal values between two consecutive sampling signals. Because a characteristic of a sound signal is relatively similar to a characteristic of a sinusoidal wave, a signal distortion often occurs on a frequency-lowered signal if interpolation signal values are calculated by a common method for calculating arithmetic mean. Furthermore, during the conventional operation for overlapping the signal frames, whether their phases match to each other is usually not taken into consideration. Therefore, a condition where a part of the signals are added while another part of the signals are subtracted may occur on an overlapping section to cause the signal distortion. Worth yet, the signal distortion becomes even more serious as a magnitude for lowering frequency gets larger.